The present invention relates, in general, to a bumper for a motor vehicle.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Bumpers are typically arranged across the front and rear of a motor vehicle between the plastic shell of the vehicle body and the frame of the motor vehicle. To prevent damage to the vehicle body structure in the event of a crash or impact at low speed, crash boxes are integrated to absorb energy caused by the impact and to convert the energy in deformation work.
German Offenlegungsschrift DE 42 38 631 A1 discloses a shock absorption device for absorbing the impact energy between a bumper and a vehicle body frame, having an inner tube and an outer tube which move within one another in the event of a collision. The inner tube is mounted to the legs of the cross member. This construction is heavy and complicated.
U.S. Pat. No. 6,520,552 describes a bumper for a motor vehicle, including a cross member having a U-shaped cross section and attached to side rails of a vehicle chassis. The cross member includes a web and two legs connected to the web. Received in the cross member is a crash box which has a cross member proximal end joined to the web and to confronting ends of the legs.
U.S. Pat. No. 5,785,367 discloses a bumper having a cross member extending transversely to side rails of a vehicle body, and crash boxes integral with the cross member. Cross member and crash boxes are joined through welding for example.
Welding the end of a crash box to the cross member about the entire circumference of the crash box is difficult to implement in view of the limited accessibility to the crash box end. Therefore, it has been proposed to omit a welding of the upper and lower horizontal legs of the crash box to the cross member. This, however, adversely affects deformation of the crash box. Practice has shown that the behavior of the crash box in the contact area of the non-welded upper and lower horizontal legs of the crash box is unpredictable so that a reliable assessment of the crumpling behavior of the bumper has been impossible to foresee in the event of an impact.
German Offenlegungsschrift DE 102 06 011 as well as DE 101 35 903 A1 disclose bumpers having a cross member having areas which are bulged inwardly in an attachment area with the crash boxes.
It would be desirable and advantageous to provide an improved bumper to obviate prior art shortcomings and to exhibit improved yielding capability.